RHA serves as partial replacement to cement in order to provide an economic use of the by product, reduceRHA waste deposit and consequently produce strong and durable concrete at a cheaper cost. This papertherefore presents the fracture behaviour of concrete made from Ordinary Portland Cement with Rice-Husk Ash(RHA) made from a rice paddy replacement up to the age of 28 days. Six different replacement percentages ofcement by RHA, (i.e. 0%, 10%, 15%, 20%, 25% and 30%) were used for the concrete specimens. The resultsare compared with those of concrete without RHA (i.e. 0% RHA and 100% OPC). The weight was measured foreach sample specimen for each RHA % level (0, 10, 15, 20, 25, and 30) and for the number of days for settingof the concrete block cubes (7, 14, 21 and 28). Compressive test was carried out by applying a constant uniformpressure through the testing machine on the cubes of the concrete blocks until failure occurs. Results show thatthe more Rice Husk Ash used in the concrete mix, the lighter the finished concrete becomes, the higher the daysof setting of the concrete, the more the compressive force needed to break the block, also, the higher thereplacement level of the Rice Husk Ash up to 30 %, the stronger the block. The significance of the study is thatRHA therefore provides a positive effect on the mechanical strength of concrete mix, up to 30 % Rice Husk Ashreplacement up to the age of about 28 days and reduction in utilization of cement, and expenditures. Furtherexperiment should be performed to test the mechanical strength of concrete mix, beyond 30 % Rice Husk Ashreplacement above the age of about 28 days.

Cement, as a binder, is the most expensive input in tothe production of sand Crete blocks (Hornbostel,1991). Ordinary Portland cement is acknowledged asthe major construction material throughout the world.The production rate is approximately 2.1 billiontons/year, and is expected to grow exponentially toabout 3.5 billion tons/year by 2015 (Coutinho, S. J.,2003). From 1880 to 1996, the world’s annualconsumption of

Portland cement rose from 2 milliontons to 1.3 billion tons. This is associated with majorenvironmental issues which include: cementmanufacturing is the third largest CO2

producer andthis accounts for over 50 % of all industrial CO2

emissions (for every ton of cement produced, 1.25ton of CO2

is released to the air); 1600 ton of naturalresources are consumed to produce 1 ton of cement(Muga, et al., 2005). This calls for the use ofsustainable binders. One of the most promisingmaterials is rice huskash (RHA).

According to(Stroven et. al, 1999) the use of ricehusk ash in concrete was patent in the year 1924 upto 1972, and (Deepa et. al, 2006) reported that all theresearches were concentrated to utilize ash derivedfrom uncontrolled combustion. (Nehdi et. al, 2003) intheir experiment also concluded that controlledcombustion influence the surface area of RHA, sothat time, temperature and environment to beconsidered to produce ash of maximum reactivity.

Rice husk is an agricultural residue from the ricemilling process. The chemical composition of ricehusk vary due to the differences in the type of paddy,type of fertilizer used, crop year, climate andgeographical conditions (Chandrasekhar, et al.,2003). The husk of the rice is removed in the farmingprocess before it is sold and consumed. It has beenfound beneficial to burn this rice husk in kilns tomake various things. The rice husk ash is then usedas a substitute or admixture in cement. Therefore theentire rice product is used in an efficient andenvironmentally friendly approach. The producedpartially burnt husk from the milling plants whenused as a fuel also contributes to pollution and effortsare being made to overcome this environmental issueby utilizing this material as a supplementarycementing material (Chandrasekhar, et al., 2006).Disposal of rice husk ash is an important issue inthese countries which cultivate large quantities ofrice. Rice husk has a very low nutritional value andas they take very long to decompose arenotResearch Journal in Engineering and Applied Sciences

appropriate for composting or manure. Burning thehusk under controlled temperature below 800 °C canproduce ash with silica mainly in amorphous form(Zhang, and Malhotra,1996).The 100 million tons ofrice husk produced globally begins to impact theenvironment if not disposed of properly. Oneeffective method used today to rid the planet of ricehusk is to use it to fuel kilns. Burning the rice husk isan efficient way to dispose of the rice cultivation by-product while producing other useful goods. The ricehusk ash is a highly siliceous material that can beused as an admixture in concrete if the rice husk isburnt in a specific manner. The presence of mineraladmixtures in concrete is known to impart significantimprovements in workability and durability. Thecharacteristics of the ash are dependent on thecomponents, temperature and time of burning (Chao,et al., 2008). During the burning process, the carboncontent is burnt off and all that remains is the silicacontent. The silica must be kept ata non-crystallinestate in order to produce an ash with high pozzolanicactivity. The presence of silica in this pozzolanicmaterial makes possible the use of rice husk ash toreplace part of cement (Chandrasekhar, et al., 2003).The ash, which has no useful application, is usuallydumped directly in the environment and causespollution and air contamination. The rice huskthereby constitutes an environmental nuisance as theyform refuse heaps in the areas where they aredisposed.

The objective of this work is therefore to investigateinto the mechanical strength of concrete by mixingwith rice husk ash since the use of these by-productsis an environmental-friendly method of disposal oflarge quantities of materials that would otherwisepollute the land,water and air. And to serve as apartial replacement to cement which will provide aneconomic use of the by–

product and consequentlyproduce strong and durable concrete at a cheapercost.

MATERIALS AND METHODS

Ordinary Portland® Cement (OPC) conforming

toASTM C 150 type I was used for this study, itschemical and physical properties are given in Table1.

Production Of The Block Samples Using OrdinaryPortland Cement(OPC)

For the purpose of this work, 150 mm x 250 mm x450 mm hollow blocks were produced. The quantitiesof materials obtained from the mix design weremeasured using a weighing balance. The cement,RHA and sand were then mixed together to obtain ahomogeneous mixture. Measured volume of waterwas then poured on to the mixture using bucket.

Ashovel was used to mix the mixture to get therequired workability. A steel hollow mould was usedto mould the blocks. The block samples were curedby sprinkling water every 12 hours.

Production of Rice Husk Ash

The rice husk used in this work husk was

collectedfrom paddy field in Ibadan, Nigeria. It was then burntin the laboratory by using a ferro-cement withincinerating temperature of about 700°C. The ash wascollected and ground in a mill for about 180 minutes.X-Ray Diffraction analysis was performed todetermine the silica form of the produced Rice HuskAsh (RHA) powder samples using an X-raydiffractometer. Figures 1-

4 show the pictures ofRHA before grinding, when burnt, after grinding andunder electroscope respectively.

In this work, six batches of concrete were producedwith varying amounts of Rice Husk Ash substitutedfor Ordinary Portland Cement. There was a controlgroup with no rice husk ash i.e. 0 % replacement,then followed by 10% replacement, 15%replacement, 20% replacement, 25% replacement and30% replacement. This is important because it fits theconditions of rural and developing countries, wherecement is expensive and rice cultivation ispredominant.

COMPRESSION TEST

The compression tests for the concrete cubes werecarried out at the Fracture Mechanics Laboratory ofMechanical Engineering Department, University ofIbadan, Nigeria. Standard test procedures were usedfor the experiment. Before the commencement of thetest, all specimens were weighed and the resultsrecorded and at the time of each respective test. Theweight was measured for each sample specimen foreach RHA % level (0, 10, 15, 20, 25, and 30) and forthe number of days for setting of the concrete blockcubes (7, 14. 21, 28). A constant uniform pressure

was applied by the testing machine to the cubes of theconcrete blocks until failure occurs. Cracks wereinitially noticed on the specimen and the crackspropagated until failure was finally observed whenthe cube no longer could resist the force appliedto itwithout breaking apart. Results of the experiment areshown on table 2.

Figure 6. Graph of Compressive Strength againstNumber of Days for setting

X-ray diffractometer analysis showed that the RiceHusk Ash was mainly in amorphous form. And RHAhad higher surface area as shown figure 4. The resultsin table 1 show that as the number of days for settingincreases, the mass of the concrete blocks decreasesfor all batches of concrete. As the percentage of RHAincreases, the mass of concrete reduces and thecompressive strength increases. This is also evidentin figure 5. Fig. 6 also revealed that as the numberof days increases, the compressive strength increases.The compressive strength for the concrete having30% RHA is higher than the compressive strengthofconcrete having 0% RHA.

CONCLUSION

The more Rice Husk Ash that is used in the mix, thelighter the finished concrete becomes. Replacementup to 30% of cement with Rice Husk Ash causesreduction in utilization of cement, and expenditures,also can improve quality of concrete at the age ofmore than 28 days.

According to this study, addition of pozzolanicmaterials like rice husk ash to the concrete, canimprove the mechanical strength of concrete. Thespecimens with silica extracted from Rice Husk Ashshowed higher compressive strength values whencompared with their equivalent mixture without RiceHusk Ash for up to 30% replacement and the age of28 days.

ACKNOWLEDGEMENT

The authors are grateful to Prof. I. A. Adetunde,Dean, Faculty of Engineering, University of Minesand Technology, Tarkwa for his valuable advice inthis work.